A spark plug generates spark discharge in a gap between a center electrode and a ground electrode to realize ignition of an air-fuel mixture in a combustion chamber of an internal combustion engine. As a ground electrode of a spark plug, ground electrode has been known in which an electrode tip is joined to an electrode base material in order to improve wear resistance of the ground electrode against spark discharge and oxidation (refer to Patent Document 1, for example). The electrode tip of the ground electrode is made of a material whose wear resistance against spark discharge and oxidation is superior to those of the electrode base material. Examples of the material of the electrode tip include a noble metal (e.g., platinum, iridium, ruthenium, or rhodium), nickel, and an alloy composed mainly of any one of these metals. In the ground electrode including the electrode tip joined to the electrode base material, a fusion zone containing the component of the electrode base material and the component of the electrode tip is formed due to welding for joining the electrode tip to the electrode base material.